VoIP (Voice over Internet Protocol) systems employ various methods and protocols to notify system users when a triggering event arises, such as the receipt of a voicemail message associated with a particular telephone extension. For example, IP (Internet Protocol) voicemail systems may send MWI (Message Waiting Indicator) notifications to their associated PBX (Private Branch eXchange) systems to identify such voicemail messages. Existing IP voicemail systems generally send MWI notifications to all of their associated PBX systems, regardless of whether an extension associated with the MWI notification actually resides on a PBX system.